A semantic file system is an information storage system that provides flexible associative access to the system's contents by automatically extracting attributes from files with file type specific transducers. Associative access is provided by a conservative extension to existing tree-structured file system protocols, and by protocols that are designed specifically for content based access. Compatibility with existing file system protocols is provided by introducing the concept of a virtual directory. Virtual directory names are interpreted as queries, and thus provide flexible associative access to files and directories in a manner compatible with existing software. Rapid attribute-based access to file system contents is implemented by automatic extraction and indexing of key properties of file system objects. The automatic indexing of files and directories is called "semantic" because user programmable transducers use information about the semantics of updated file system objects to extract the properties for indexing. Experimental results from a semantic file system implementation support the thesis that semantic file systems present a more effective storage abstraction than do traditional tree structured file systems for information sharing and command level programming.

Recent growth of the Internet has greatly increased the amount of information that is accessible and the number of resources that are available to users. To exploit this growth, it must be possible for users to find the information and resources they need. Existing techniques for organizing systems have evolved from those used on centralized systems, but these techniques are inadequate for organizing information on a global scale. This article describes Prospero, a distributed file system based on the Virtual System Model. Prospero provides tools to help users organize Internet resources. These tools allow users to construct customized views of available resources, while taking advantage of the structure imposed by others. Prospero provides a framework that can tie together various indexing services producing the fabric upon which resource discovery techniques can be applied.

This thesis presents a new architecture for information discovery based on a hierarchy of content routers that provide both browsing and search services to end users. Content routers catalog information servers, which may in turn be other content routers. The resulting hierarchy of content routers and leaf servers provides a rich set of services to end users for locating information, including query refinement and query routing. Query refinement helps a user improve a query fragment to describe the user's interests more precisely. Once a query has been refined and describes a manageable result set, query routing automatically forwards the query to relevant servers. These services make use of succinct descriptions of server contents called content labels. A unique contribution of this research is the demonstration of a scalable discovery architecture based on a hierarchical approach to routing.

We describe the first system that provides query based associative access to the contents of distributed information servers. Queries describe desired object attributes, and are automatically forwarded to servers that contain relevant information. In typical distributed information systems there are so many objects that underconstrained queries can produce large result sets and extraordinary processing costs. To deal with this scaling problem we use content labels to permit users to learn about available resources and to quickly formulate queries with adequate discriminatory power. We present experimental data that show that certain content label attributes can be automatically chosen. We have implemented associative access to a distributed set of information servers in the content routing system. A content routing system is organized as a network of servers called content routers that present a single query based image of a distributed information system. Experiments motivated by our video access service show that substantial performance benefits result when content routers are removed from the client-server path once an object of interest is found.

1 Introduction The Internet contains over one million hosts that provide file service and other information servers specializing in topics such as news, technical reports, biology, geography, and politics. The Internet's vast collection of servers can be viewed as a distributed database containing a wealth of information. Unfortunately, this information is relatively inaccessible because there is no mechanism for browsing and searching it associatively. The difficulty of providing associative access to a large number of distributed information servers lies primarily in problems of scale. The scale of the Internet, which is today only a fraction of its eventual size, is so great as to render infeasible any comprehensive indexing plan based on a single global index. In addition, the cost of distributing a query throughout the Internet is prohibitive. Finally, in very large scale systems, the number of results to a typical user query is incomprehensibly large. For these reasons, we expect that efficient associative access will require both content routing and query refinement. Content routing is the process of directing user queries to appropriate servers. Query refinement helps a user formulate meaningful queries. These query services can be implemented by a content routing system that will:

Users often find that local resources are too limited to solve large computing problems. At the same time, unused machines remain inaccessible because of incompatible architectures, ignorance of their capabilities, or incompatible administrative restrictions. To preserve this investment in equipment, yet allow for the solution of large problems, mechanisms are needed to join these systems into cooperating groups across the boundaries of administrative domains and physical locality. In this paper, we describe messiahs, a system intended to provide scalable mechanisms for the efficient implementation of scheduling policies on distributed systems, while preserving the autonomy of the component systems. These systems can range from a few workstations to hundreds of heterogeneous, autonomous systems interconnected via networks ranging from local-area networks to geographically large networks, connected by arbitrary links. This work was supported by a NASA Graduate Student Researchers Fell...

This handout is about orderly ways of naming complicated collections of objects in a computer system. A basic technique for understanding a big system is to describe it as a collection of simple parts. Being able to name these parts is a necessary aspect of such a description, and often the most important aspect.

A semantic provides le system is an information storage system that exible associative access to the system's contents by automatically extracting attributes from les with le type speci c transducers. Associative access is provided by a conservative extension to existing tree-structured protocols, and by protocols that are designed speci le system cally for content based access. Compatiblity with existing le system protocols is provided by introducing the concept of a virtual directory. Virtual directory names are interpreted as queries, and thus provide exible associative access to les and directories in a manner compatible with existing software. Rapid attribute-based access to le system contents is implemented by automatic extraction and indexing of key properties of le system objects. The automatic indexing of les and directories is called \semantic " because user programmable transducers use information about the semantics of updated le system objects to extract the properties for indexing. Experimental results from a semantic le system implementation support the thesis that semantic le systems present a more e ective storage abstraction than do traditional tree structured le systems for information sharing and command level programming. 1